Wood preservative



Patented Apr. 12, 1938.

UNITED STATES PATENT OFFICE woon PRESERVATIVE No Drawing. ApplicationOctober 29, 1936, Serial No. 108,307

5 Claims.

The invention relates to wood preservatives and has as an object theprovision of a wood preservative produced by the hydrogenation of pitch,particularly coal tar pitch, or coal tar residuum boiling abovesubstantially 350 C.

The most commonly used wood preservative is that known in the art ascreosote and is usually derived by distillation of tar resulting in themanufacture of coke from soft coal. The said creosote is distilled fromthe tars, under present practice at temperatures from substantially 200C. to 400 C.

It is well understood that a distillate taken off at temperaturesstarting above 350 C. have substantially no toxic value and is thereforesubstantially useless as a wood preservative, at least insofar asdestroying rot-producing fungi or fungoids.

I have discovered that if coal tar pitch, including thereby any residuumboiling above substantially 350 C'.,'having no, or extremely small,toxic value be subjected to a process of hydrogenation to induce lowerboiling fractions, and these fractions be distilled off within the range0 for wood preservative, as above stated for natural creosote, the woodpreservative thus produced will have toxic value equal or superior tothe natural creosote removed from the same initial coal tar from whichthe pitch thus treated was secured at the same distillation range. Testsdown to date prove such an advantage to the extent of substantiallytwo-fold.

The tests referred to show that a concentration of one-half of one percent of natural creosote distilling 22 per cent below 270 C. was required for total inhibition of growth of fungi or fungoids, while aconcentration of one-quarter of one per cent was, required in the caseof the material of the present invention having the same boiling range.In the case of material distilling 37 /2 per cent below 270 C. therequired concentrations were one quarter of one per cent and one eighthof one per cent respectively, for natural creosote and that of thepresent invention.

The product of the invention is a wood preservative falling within thespecifications of the creosote of trade when produced by hydrogenationof a residuum of coal tar for this purpose. At present thesespecifications call for a material evaporating not more than 5% at 210C. and having a high boiling point of 400 C. The residue left whendistilled at 355 C. does not usually exceed 50%.

Since the material of the present invention is a product of the processdescribed and claimed in my copending 'application'Serial No. 14,378,filed April 2, 1935, now Patent No. 2,082,885, issued June 8, 1937, forMethod of producing a wood preservative or the like, by which processthe resulting material may be varied in accordance with the requirementsof the trade, it is within the present invention to depart to someextent from the specific boiling points and distillation ranges givenabove as shall from time to time be required by commercial change ofrequirements even to the extent of including fractions boiling as highas 500 C. as set forth in said patent.

Briefly stated the product of the present invention is a hydrogenationproduct of a coal tar residuum boiling substantially above 350 C., saidhydrogenation product consisting of fractions boiling betweensubstantially 200 and 500 C., having a specific gravity between 1.003and 1.10 and having suitable toxic properties for use as a woodpreservative. The residue, when the product is distilled at 350, can bemade as low as desired by the process of my Patent 2,082,885, but shouldnot exceed 50%.

An important discovery of the present invention is that hydrogenation ofpitch to produce wood preservative falling within the boiling pointranges of creosote induces new toxic properties therein. I am unable todefine the chemi cal differences between the synthetic creosote of a theinvention and the natural creosote distilled from the initial coal tar.Therefore it seems at present impossible to formulate adequate claims tothe product embodying the invention except by referring to the processby which it is produced.

The product of the present invention may be produced by hydrogenation ofcoal tar pitch as known to the trade. It may equally well be produced bysimilar treatment of a residuum from distillation of creosote derived bydistillation of coal tar, in cases where the creosote was taken underconditions to include too high a residuum boiling at or above 350 C. Therefining of such unacceptable creosote leaves a residuum which may ormay not be denominated pitch by the trade but is a material which may behydrogenated to produce the product of the present invention having thenecessary toxic properties and other characteristics required for a woodpreservative impregnant.

Minor changes may be made in the physical embodiment of the inventionwithin the scope of the appended claims without departing from thespirit thereof.

I claim:

1. A wood preservative consisting of a liquid hydrogenation product ofcoal tar residuum boiling above substantially 350 C., said productconsisting of fractions having boiling points falling between 200 C. and500 C., and having suitable toxic properties for the purpose indicated.

2. A wood preservative consisting of a liquid hydrogenation product ofcoal tar residuum boiling above substantially 350 C., said productconsisting of fractions having boiling points falling between 200 C. and500 C., the specific gravity of the fluid being between 1.003 and 1.10,and having suitable toxic properties for the purpose intended.

3. A wood preservative consisting of a liquid produced as a result ofhydrogenating coal tar residuum boiling above substantially 350 C.,having substantially no toxic properties, said liquid consisting offractions having boiling points falling between 200 C. and 500 C., and.having suitable toxic properties for the purpose indicated.

4. As a Wood preservative, a toxic liquid hydrogenation product of coaltar residuum boiling substantially above 350 C., said product consistingof fractions boiling between 200 and 400 C., evaporating not more than5% at 210 C., and having a residue resulting from distillation at 355 C.of not more than 50%.

5. As a wood preservative, a toxic liquid obtained by hydrogenating theresiduum of coal tar after removal of commercial creosote therefrom,said product having a toxic value of substantially twice that of thecreosote removed from said residuum, and consisting of fractions boilingbetween 200 C. and 400 0., evaporating not more than 5% at 210 C. andhaving a residue resulting from distillation at 355 C. of not more than50%.

JACQUELIN E. HARVEY, JR.

